Study of Antarctic ice cores reveals atmospheric CO2 history over past thousand years

by Bob Yirka , Phys.org

Credit: Newcastle University

(Phys.org)—A small team of researchers with affiliations to institutions in the U.S., Switzerland and Korea has found links between atmospheric carbon dioxide levels, the land carbon reservoir and climate over the past thousand years, by examining ice cores taken from the West Antarctic Ice Sheet Divide. In their paper published in Nature Geoscience, the team describes the levels of CO2 they found and why they believe that most of the level changes they observed were likely due to terrestrial sources. Jed Kaplan, with the University of Lausanne offers a News & Views piece on the work done by the team in the same journal issue, comparing CO2 level changes found by the researchers with historical human events putting the ice core data into perspective.

To learn more about atmospheric carbon levels over the past millennium the researchers analyzed ice core samples taken by workers on the Antarctic WAIST Divide Ice Core project—looking for both CO2 concentrations and their isotopic composition. In so doing they were able to see levels rise and fall at both decadal and centurial level of detail, for the years 760 to 1850. The data showed two main "events" during that period, the first was a slow decline running from the start of the twelfth century to the start of the nineteenth century—the other was decadal level ups and downs of levels attributable to unknown, but speculative causes. The researchers also believe that most of the level changes came about due to terrestrial sinks and sources, not activity in the oceans.

Kaplan suggests some of the ups and downs could be traced back to natural causes, such as increases or decreases in peat deposits due to temperature variations, though they could just as easily be blamed on human activities such as soil erosion in Eastern Europe due to agricultural activities. He also points out that the sharp drop in CO2 levels that occurred around 900, almost undoubtedly came about due to population drops in Mesoamerican cultures after the introduction of European diseases. Likewise the sharp increase in carbon levels from 975 to 1080, can almost certainly be attributed to events in both Europe and Asia. He also notes a dip right around the time shortly after the onset of the Black Plague, which happened to coincide with widespread draughts in Asia. He concludes by suggesting that studies of ice cores such as that done by this new team not only help reveal trends in the past, but will likely prove useful for helping to predict trends in the future.

The stability of terrestrial carbon reservoirs is thought to be closely linked to variations in climate, but the magnitude of carbon–climate feedbacks has proved difficult to constrain for both modern and millennial timescales. Reconstructions of atmospheric CO2 concentrations for the past thousand years have shown fluctuations on multidecadal to centennial timescales, but the causes of these fluctuations are unclear. Here we report high-resolution carbon isotope measurements of CO2 trapped within the ice of the West Antarctic Ice Sheet Divide ice core for the past 1,000 years. We use a deconvolution approach to show that changes in terrestrial organic carbon stores best explain the observed multidecadal variations in the δ13C of CO2 and in CO2 concentrations from 755 to 1850 CE. If significant long-term carbon emissions came from pre-industrial anthropogenic land-use changes over this interval, the emissions must have been offset by a natural terrestrial sink for 13C-depleted carbon, such as peatlands. We find that on multidecadal timescales, carbon cycle changes seem to vary with reconstructed regional climate changes. We conclude that climate variability could be an important control of fluctuations in land carbon storage on these timescales.

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Study of Antarctic ice cores reveals atmospheric CO2 history over past thousand years (2015, May 1)
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User comments

"that occurred around 900, almost undoubtedly came about due to population drops in Mesoamerican cultures after the introduction of European diseases"hold on... You are saying Europeans were introducing disease to Central America in 900CE????!!!! I am graduating with an Archeology degree in 2 weeks and In NO mesoamerica classes was anything like that even remotely suggested. Wheres your data? Because Vikings in Central America causing diseases would really be big news... At best they were no further south than MA. And don't say quexocotal either, wrong time, and only one person, and probably an albino, not a Viking (if real at all). And trade in the other direction was exclusively between isolated Siberian natives and Aleutians peoples, (and the discovery of it is a BIG deal). This is some really shotty science. No way were Europeans in Mexico 1100 years ago, and if they were, then how come they all died from european disease again 600 years later?

"that occurred around 900, almost undoubtedly came about due to population drops in Mesoamerican cultures after the introduction of European diseases"hold on... You are saying Europeans were introducing disease to Central America in 900CE????!!!!

The data has to fit into the AGW alarmist agenda, otherwise it is no good. So yes, there were primitive natives burning wood fires and their little campfires were causing catastrophic climate change all around the world! Do you see how this alarmist propaganda works?

It's hilarious to see the goobers trying to discredit the work of professionals. Do they not understand their silly semantic games only reveal more about their lack of science education than any other "truth"?

Their positions spring from political prejudice and are enabled by technical ignorance of the field.

The data has to fit into the AGW alarmist agenda, otherwise it is no good. So yes, there were primitive natives burning wood fires and their little campfires were causing catastrophic climate change all around the world! Do you see how this alarmist propaganda works?

And this has to fit your denialist conspiratorial thinking.Nowhere does it say that CO2 released by "primative natives" caused cliamte change.Just that the rising/falling levels of CO2 can be seen in the record.

This is some really shotty science. No way were Europeans in Mexico 1100 years ago, and if they were, then how come they all died from european disease again 600 years later?

I saw one of those shows on "Science" proved that there was an English person buried in the S.Western U.S. around 800 or 900 years ago, which is well before the official records of colonization and exploration of the W. Hemisphere. They were able to track down his English residence that he lived in before traveling to the western hemisphere.

The answer to your question would be that not everyone who traveled around the world had carried smallpox.

They also uncovered Viking glyphs in Central North America from around the same time period or before then.

Nowhere does it say that CO2 released by "primative natives" caused cliamte change.Just that the rising/falling levels of CO2 can be seen in the record.

The author says that a drop in CO2 was "due to population drops" (at 900 CE). Tell me oh wise one, how do they arrive at that fantastic conclusion? This is not science, it's pure speculation based on an alarmist agenda.

Nowhere does it say that CO2 released by "primative natives" caused cliamte change.Just that the rising/falling levels of CO2 can be seen in the record.

The author says that a drop in CO2 was "due to population drops" (at 900 CE). Tell me oh wise one, how do they arrive at that fantastic conclusion? This is not science, it's pure speculation based on an alarmist agenda.

Ity's not an "alarmist agenda" at all .... it's just empirical science. More people useing more fossil fuels create more atmospheric CO2. End of. Do try to look beyond your ideological world-view.

Nowhere does it say that CO2 released by "primative natives" caused cliamte change.Just that the rising/falling levels of CO2 can be seen in the record.

The author says that a drop in CO2 was "due to population drops" (at 900 CE). Tell me oh wise one, how do they arrive at that fantastic conclusion? This is not science, it's pure speculation based on an alarmist agenda.

Ity's not an "alarmist agenda" at all .... it's just empirical science. More people useing more fossil fuels create more atmospheric CO2. End of. Do try to look beyond your ideological world-view.

So people living during 900CE were burning enough fossil fuels to affect CO2 levels? What kind of oil refineries did they have back in 900CE?

It's hilarious to see the goobers trying to discredit the work of professionals. Do they not understand their silly semantic games only reveal more about their lack of science education than any other "truth"?

Their positions spring from political prejudice and are enabled by technical ignorance of the field.

I understand climate change, I also understand the current record of pre-Columbian America. And the authors of this article have made a mistake... There were no Europeans in Meso-America 1100 years ago. That is pretty indisputable. There was no die off from european disease until the 1490s at the earliest. WE ALL KNOW THIS!!! ---and mentioning it is not a "semantic mistake", it's a big one, as they give a fictious event as the cause for a shift in CO2The Mayan civilization did collapse around 900-1000CE though, and funnily enough we think a localish climate shift in rain patterns caused it... So I'll take an apology, because I am not the goober here

You folks should read more broadly. There's a typo in the above account. Just do a little googling to get an accurate description of the research. The actual dip in CO2 was centered at 1610, consistent with lag times for a) genocide after the European "discovery" of the Americas, and b) re-forestation. Disease and war would have preferentially affected settled populations engaged in agriculture rather than hunter-gatherers. Farmers died, and forests reclaimed their fields.

The earliest settlers in what is now New England marveled at the park like conditions of the forests, made that way by the practices of Native Americans. They also rejoiced that those Native Americans had been wiped out by smallpox and other ills brought by contact by European fishermen, seeing it has a sign from "God" that they were blessed.

There is no doubt about the decimation of native inhabitants of the North and South America by the intrusion of Europeans and the resulting changes in land use on a massive scale.

"He also points out that the sharp drop in CO2 levels that occurred around 900, almost undoubtedly came about due to population drops in Mesoamerican cultures after the introduction of European diseases."

The historical statement on European disease wiping out Mesoamerican cultures was obviously an error due to either the author or the quoted researcher (still the author's mistake for not catching it).Regardless, the article makes no mention of CLIMATE CHANGE. It simply states measurement tracking along with some (speculative) coincidental sources.

From your responses, it's obviously you AGW Chicken Littles.Your cult has redefined science, climate history and now human history just to propagate their CO2 lies and yet you continue to deny their fraud.

So people living during 900CE were burning enough fossil fuels to affect CO2 levels?...........

Yes.(thanks walterbrown)

Which fossil fuels were they burning at 900CE to the extent that it was affecting CO2 levels? Oil, natural gas, or coal? Wood is not a fossil fuel!

Coal. There has been a lot of metallurgy being practiced in the past few thousand years. Wood, as a heat source to practice it, didn't provide sufficient heat. Not to mention - livestock. An agrarian society (with more livestock than people) will produce a large amount of methane.I'm sure there are plenty of other reasons, too.It's why we train scientists - to document enough observations to reasonably explain a thing...

Most people understand that humans do more than burn fossil fuels to change the levels of greenhouse gases in the atmosphere. It's my understanding that thousands of years ago the primary anthropogenic cause of increases in greenhouse gases was agriculture (http://courses.wa...ge03.pdf ). As early as 8000 years ago, clearing land to grow food caused increases in CO2 levels. And ~5000 years ago, animal husbandry began to release CH4. Decreases in CO2 levels over the years was likely due to epidemics which caused some farms to revert to the original landscape. There were fossil fuels used back then (e.g., peat), but it's thought that had a smaller affect.

The notion that changes in carbon dioxide concentration is due to human activity 1100 years ago is ridiculous. Not only were there approximately 10 times less people on earth, the energy consumption was hundreds of times lower per person. For comparison: we consume about 4,2 billion metric tons crude oil per year and another ~7 billion metric tons of coal per year. Now tell me, how could the peasants of the time come even close to this?

Note that I am not taking on a stance on the AWG issue, but I hate really stupid inventions of "facts"..

Did you bother to read the linked paper? Note a couple things here - we're not talking about anything close to what's currently happening. The changes in CO2 show a rise of ~20ppm over ~6000 years. That's compared to a further rise of ~120 over a few decades. So deforestation over large areas of the earth can cause changes over thousands of years. How, exactly, is that unbelievable?

The authors of the article did not claim that 6000 years of human activity caused an increase of carbon dioxide in the atmosphere. They said that a peak "coincided" with some human disaster 1100 years ago. Get it?

About human activity. You have to provide the proof, not I. It's the same situation as when an astrologist wants proof that jupiter does not influence the character of newborns, that the position of venus does not bring about special circumstances for marriages, a.s.o.

I do not have the time to read a fringe paper, bring the arguments here. Let's hear it: what areas are talking about, what mass of biomatter are we talking about? And what about vulcanoes? Sell the idea right here...

The notion that changes in carbon dioxide concentration is due to human activity 1100 years ago is ridiculous.

This is a statement without any evidence. And without any evidence, this is a textbook example of the fallacy of personal incredulity.

Not only were there approximately 10 times less people on earth,

By itself, of course, this is meaningless unless you can state why the population precludes human influence on CO2.

the energy consumption was hundreds of times lower per person.

Ah, now we get to the meat of your claim. But, of course, energy consumption had little or nothing to do with their claims. I can only see the first page, but it seems they are talking about changes in biosphere and that pretty much points to land use change.

So your evidence didn't show, in any way, that the concept was ridiculous. It was only your inability (or unwillingness) to understand the idea of land use change as causing changes in atmospheric green house gases that allowed you to make your initial statement, which is, as I mentioned, pretty much a textbook example of the fallacy of personal incredulity.

They said that a peak "coincided" with some human disaster 1100 years ago.

Actually, they didn't. If you read the 1st page (you can access that for free), they make a point of saying the CO2 level was stable from 750-950 and showed a slight increase after that. It was pretty obvious for anyone familiar with the hypothesis that the above story was in error. Which is one reason you should take any media story with a large grain of sand and try to check out the actual paper. And I thought the comments above yours had already worked that out.

Actually, I don't. But think about it for a moment without your bias: We have a large area of farming established in the tropics - an area that we know is very important in the carbon cycle. It would seem to be quite unreasonable to believe that clearing a sizable area of land in that region would not impact the natural carbon cycle. So, unless the carbon cycle is irrelevant to the amount of CO2 in the atmosphere (it isn't), it would be astoundingly unlikely that the rise of agriculture would have no effect.

I do not have the time to read a fringe paper, bring the arguments here.

Umm, this is hardly a "fringe paper" - it's a paper that appeared in a major journal and has been cited over 800 times. Argument from ignorance (which is the fallacy you demonstrated with your comment) is similar to the fallacy of personal incredulity. Just so you know ;).

I read a lot of argument about why I am the victim of a "fallacy", but precious little in terms of numbers. So far, I have - from your above statements - a 20 ppm increase from 6000 years of human activity, but nothing about the land area that you believe has been affected by some depopulation of humans, no mention of how many PPM of CO2 that equates to. It is all about the numbers, and you present none.

About your lack of numbers. I don't consider "slight increase", or "stable level" to contain any useful information. Here is one piece of information for you: every PPM of CO2 weidhts about 8 Gton. When I look at the population graph here: http://upload.wik...e%29.png

I see only temporary population setbacks. Is it plausible, that these short termed "dips" can integrate into gigatones of carbon? And once the population has rebounded, should not the sequestered carbon have been released again? Presumably, the "new" and equally numerous humans need just as much farmland as the "old" one..? Here is your cue to present your numbers, if you have any..

About the quality of the article. I don't have a problem with their method of determining the CO2 concentration, nor (in principle) their method to try to use the C13 concentration to unravel contributions to different sources. My problem is the fact (if the above review is truthfull) that they fellt compelled to speculate that the variations were caused by human activities. It's this last bit that soils the whole article.

Note, however, that I cannot judge the validity of their deconvolution since I only have access to the first page. I only give my approval to the principle of using C13 concentration to untangle the different contributions..

So you need your knowledge to be spoon fed? Being intellectually lazy is a good way to let people manipulate your beliefs. If the science is of interest to you (which it seems to be since you commented here so emotionally), you should be going out and reading these papers yourself and not letting anyone fool you with nonsense.

Anyway, had you bothered to read the paper I linked to, you'd find he accounts for 220-245GtC for clearing land and a further 10GtC for burning peat. I don't think it perfectly explains all the CO2 increase, but it shows that humans are likely the cause for the great majority of increase in CO2. Similar work shows that reforestation due to the plague explains much of the decrease in CO2 for 1500-1800.

About the quality of the article. I don't have a problem with their method of determining the CO2 concentration, nor (in principle) their method to try to use the C13 concentration to unravel contributions to different sources. My problem is the fact (if the above review is truthfull) that they fellt compelled to speculate that the variations were caused by human activities. It's this last bit that soils the whole article.

Not having read the paper, I won't comment on how good it is. But I'm not sure why you claim that it "soils the whole article". Extending previous research is what science is all about. Piggybacking off mainstream science like Ruddiman's doesn't "soil" an article.

Improvement! Now you only use 5 rows to comment on me and use a whopping 8 rows to comment on the issue!

Where on the first page do you read that he accounts for 220-245 GtC (gigatonnes coal?) with land clearing? Care to cite the row and column? All I read is the following at the very bottom of the page: "Organic land carbon de-creases by 20 GtC from 950–1100 CE and increases by 50 GtC....". I.e. the land looses that much carbon by some mean (man or other).

No, the article does not further the science by speculating about causes that it has no evidence for. Every bit of progress that the article may or may not bring is in the quality of measurements of CO2, C13 contents and the idea to use the quota of C13 to C12 to dissentangle the different contributions. They should have stopped talking when they ran out of results. But pehaps speculating about the "right" causes may actually have helped their article to get published....?

To make it clear: the article does not seem (judging by the review above, the abstract and the first page) to have any evidence that the increase/decrease of carbon release from land has anything to do with human activities. It does present evidence that land may have released/absorbed carbon at different rates at different times, but not that this has anything to do with humans.

Furthermore, it does not seem like the authors even bother to make some back-of-napkin-calculations about population variations and their effect on CO2-levels. And that is shoddy science.

Improvement! Now you only use 5 rows to comment on me and use a whopping 8 rows to comment on the issue!

Can you state why the number of lines in a comment is relevant?

Where on the first page do you read that he accounts for 220-245 GtC (gigatonnes coal?) with land clearing?

Ok, obviously you haven't followed the discussion. My apologies if I wasn't clear. Let's recap:1. A number of people discussed fossil fuel as the reason behind the CO2 level change.2. I mentioned that, in fact, the anthropogenic changes in CO2 prior to the industrial age were thought to be primarily due to rising agriculture and I linked to Ruddiman 2003.3. Directly after my comment, you ignored all that and made the silly "ridiculous" comment.4. I pointed out that your comment was a fairly common logical fallacy.5. You disagreed.6. I pointed out that your comment contained no evidence to justify your "ridiculous" statement, so your comment was a logical fallacy.

7. You asked for numbers supporting the idea that the growth of agriculture had caused changes in CO2.8. I quoted numbers from Ruddiman 2003 which give strong evidence that for the last ~8000 years, the rise of agriculture has reversed the natural decline in atmospheric CO2 and caused CO2 levels to increase. I also pointed out that the data supported the idea that global disease from about 1500-1800 resulted in a temporary decrease in CO2 levels. Note that the paper discussed by this article (Links between atmospheric carbon dioxide, the land carbon reservoir and climate over the past millennium, Bauska et al 2015), references Ruddiman 2003 (see reference 13), so it seems likely that the paper builds on Ruddiman 2003. Regardless, we see that human involvement in the increase in CO2 going back to ~8000 years ago is mainstream science.

One thing to say about Ruddiman 2003: I don't know if this qualifies as a theory at this time. I think the evidence is strong for the CO2 portion, but I don't know if the evidence is strong enough to move it from a hypothesis to a theory. The evidence for the CH4 rise seemed a bit weaker in Ruddiman 2003. The argument was reasonable, but there seemed more hand waving in that portion. I understand some of this has been addressed in Ruddiman et al 2011 (which I need to read), so this problem may be resolved. Still, with over 800 cites (and I'm not aware of much controversy on the CO2 section), I think the idea that CO2 increases from ~8000 years ago was mainly due to anthropogenic causes would have to be considered mainstream science.

I think the evidence is strong for the CO2 portion, but I don't know if the evidence is strong enough to move it from a hypothesis to a theory.

I think it certainly qualifies as a theory and this article just makes that point so much clearer.What is your hesitation? From what these scientist report, it looks pretty clear that global CO2 levels and human activity correlate pretty well. If temperatures respond in kind, which they will, the theory is proven IIMHO.

About the time fram 8000 years. If you look at the populartion graph here : http://upload.wik...%29.png, you will notice that up until 4000 BC, the global population numbered less than 7 million. Why is this important? Well, we can imagine two extremes, where the first is that cleared land never grows back, and the second is that cleared land grows back extremely quickly.

In the first case, the aggregated man made carbon release from land is proportional to the population integrated over time (presuming that the amount of land clearing per person and year is constant). In the second case, the carbon release from land at any given time is simply proportional to the population.

What do we get from this? In the first case (cleared land never grows back), we get a function that is always increasing with time, and population dips only result in a smaller increase per unit of time. But this is not consistent with the idea that land released carbon dioxide decreased 1500-1800. In fact, it is not consistent with any reduction of land release of carbon through human activity.

In the second case (cleared land grows back almost instantaneously), the release carbon from land is increasing as population is increasing. When there is a "dip" in the population, there is an exact mirror "dip" in the release of carbon from land. And, when the population recovers, there is a corresponding recovery of carbon release from land. But we see no 300 year "dips" in the population, so also this extreme is inconsistent with a decrease in carbon dioxide release from 1500-1800.

Both ends of models contradict your claim of the 300 year (land) carbon release slump.

Interestingly, both models also make it unlikely that the time span 10 000 BC to 4 000 BC is even remotely as important as the time span 4000 BC to 1700. The integral of population over time (first model) is ~20-40 times larger for the later period. And, the instantaneous population is always at least 10 times larger in the later period. So why bother looking at the population pre 4000 BC?

Is this reasoning correct? Well, the population graph that I reference to shows only minor population slumps that last no longer than ~100 years. Perhaps this population estimate is not correct? Also, you mentioned above that 245 GtC comes from land clearing, and 10 GtC from burning fosil fuels by the primitive man. This is the main idea for concentrating only on land clearing in my reasoning.

Could it be that these numbers are not correct, or possibly that some other human (pre-industrial) activity is the main driver of carbon release? Or did land clearing per capita in fact increase over time? Decrease..?

Well, if you disagree, then it is your job to bring the arguments here, and put them on in a comment. Bring the numbers, bring the arguments..!!

I think it certainly qualifies as a theory and this article just makes that point so much clearer.What is your hesitation?

I don't think Ruddiman's closed the budget completely. So I don't think things have been answered completely. Don't get me wrong - I don't think there's any real question about whether the development of human agriculture is the primary cause of the anomalous rise in CO2 starting ~8000 years ago, but I don't think we know the whole story yet. Think of it as a hypothesis with a lot of evidence supporting it.

If temperatures respond in kind, which they will, the theory is proven IIMHO.

Now your talking about the relationship between CO2 levels and temperature. That's different than what this article is discussing. The relationship between CO2 levels and temperature is almost certainly more than a theory - the evidence for that is so overwhelming.

Because the anomaly starts ~8000 years ago. If you can't explain how an anomaly starts, you probably can't explain the anomaly at all.

Perhaps this population estimate is not correct?

Could it be that these numbers are not correct, or possibly that some other human (pre-industrial) activity is the main driver of carbon release?

So it's almost certainly the case that the numbers are wrong. Ruddiman's numbers are definitely estimates and ancient population numbers are impossible to get right. There are certainly going to be error bars. However, I think we can say pretty conclusively that the rise of agriculture was primarily responsible for the anomalous rise in CO2 that started ~8000 years ago. Could there have been other causes? Almost certainly, but the evidence is pretty clear in showing that agriculture was the main one.

Now about the drop in CO2. Ruddiman accounts for a large part of the drop, but not all of it - so disease was clearly a factor. But is there something else? Well, consider that Ruddiman's paper is from 2003 - that's pretty old. There's been a lot of evidence recently on the importance of Amazon rainforests in carbon sequestration, so Ruddiman's estimates of sequestration in America were probably too low. Remember that ~1500, 85-90% of the native americans were killed by disease. A whole civilization collapsed and most of the land deforested for cities, roads, and agriculture reverted to rainforest. At the same time that America lost ~50 million people, China lost ~20 million. And with recent numbers, perhaps more of the budget is closed for the CO2 loss that started ~1500.

And that looks like it might be correct. Ruddiman 2003 estimates ~5-10GtC sequestration due to disease in the Americas from 1550-1800. More recent estimates put that number at ~37GtC (http://www.skepti...ate.html ). So perhaps the data is sufficient now for this to be termed a theory after all. If you want to learn more about this, I suggest looking at that site (and read Ruddiman, for crying out loud - it also looks like he wrote a book last year, so I may pick that up for this summer).

Well, if you disagree, then it is your job to bring the arguments here, and put them on in a comment.

Well, of course that isn't true. Where would you get a silly idea like that? I've pointed out your fallacy (I like your more recent comments much better, by the way) and pointed you in direction of information. It's not my job to force you to educate yourself.

I'm going to see if I can dig Ruddiman out for a deeper read too. I enjoyed your cite to the skepticalscience.com website. Especially about fire man (Homo incendius). I never read much on anthropology but it's fascinating that early humans could have enough of an effect on CO2 to be seen in the antarctic ice cores measures. That is amazingly precise.

You are almost there. Now, you mention some aggregated deaths around 1500, and they can be found (it seems) in the graph that I have referenced to many times by now: http://en.wikiped...%29.png.

Although the "dip" is less than your estimated sum (where I miss references for each death toll, by the way), the population rebounds again after less than 100 years. Also notice that the population drops from ~600 to ~500 million. That is, we can at most expect a 20% decrease of man made carbon emissions for 100 years. And, if I have read you correctly, that is not what you have claimed. This is the kind of math that you have to do, but do not really bother with..

Let me guess, you think that the deaths in the amazon are more significant in terms of carbon dioxide emissions? OK, then you have to show why. You have to show me estimates of the carbon emissions per capita of amazon regions, and how the corresponding emissions in the non affected regions. With numbers. Don't forget to include an estimate of how quickly cleared land re-grows in the compared regions!

If you don't, then I have to assume that carbon emissions from clearing is roughly the same for the different regions. After all, you would expect humans to have similar calorie needs..

I also surmise that you disagree with the population curve in Wiki. Fine. Direct me to a better curve, in that case. But, the population estimate must precede the conclusions about carbon emissions. You cannot say that, well, man made carbon emissions are so certain that I am going to use them to invalidate the populations curves.

Carbon dioxide levels have varied greatly in the past. http://en.wikiped...son.jpg. That is why the rise of carbon dioxide in itself is not a proof of it's human origin, and also why the article (that we are really discussing) had good idea up to the point at which they choose to speculate about causes for which they had no proof. That is, to use the C13 fraction as an indicator of land released carbon dioxide, rather than the CO2 levels alone.

Some more details regarding population estimates and carbon emissions. If you say that population estimations are so uncertain that they cannot disprove the theory of early man made carbon emissions, you are saying that you do not need any proof at all. Because if you do not have archeological evidence of the extent of clearing - which would automatically yield population estimates - nor population estimations, you lack the very cornerstone to make your theory plausible. I hope that you understand that.

I also surmise that you disagree with the population curve in Wiki. Fine.

I really don't have a problem with the graph, per se, but for the purposes of this analysis it really doesn't work to give you enough information. You seem to be depending on it a lot, so let's discuss why it's not really relevant here. Looking at the graph, I can see at least 5 issues with it that make it useless in our discussion: provenance, labelling, error, scale, and aliasing. This will take a while, but let's look at them.1. Provenance refers where the graph came from, what data was used to create it, etc. We don't have any of that. It's just some graph on Wikipedia. I don't necessarily disagree with any of the data on the graph, but there are things missing (and things added) that make it difficult to use here.

2. Labelling is my way of saying I can't really tell when the points are occurring. I think you mentioned that you couldn't see a 300 year dip in the data (irrelevant, as it turns out and as you would have known had you read any of my links – but more on that later), but to do that you're relying on your eyes. The eyes are one of the worst instruments for analyzing data. You mention some deaths at 1500 are represented on the graph, but I'm not sure where that is. So it's really hard to say what the value is at 1500 and, as I said, the eyes usually get it wrong. But there's more to be said about the difficulty in evaluating the data here.

3a. Error refers to the error in measuring the data. All measurements have it, so what is the error here? Provenance is usually where you get that information, but that's missing here. Given the difficulties in measuring populations from hundreds of years ago, those error bars aren't going to be small. But let's use 10% as a reasonable number. As near as I can tell, the population at 1500 was ~500 million (if this confuses you, remember that population is represented on a log scale). So values of ~450 million to ~550 million would be possible for 1500.

3b. All the points would be similarly affected. If 2 adjacent points were, say, 480 million and 500 million, it would be entirely reasonable for the reality of those two points to be 520 million and 460 million, respectively. This would reverse the slope and make any analysis using these 2 points meaningless. That's one reason why scientists usually use anomalies rather than absolute values. So it impossible, using this graph to say how long a dip in the population lasted. But more on this soon.

4. Scale looks at the range of values. This graph extends over 12000 years and goes from a population of 1 million up to 10 billion. And the range we're interested extends for ~300 years and a population range of maybe 100 million. An extremely tiny section of the graph. The number of points in that range look to be 3 – 4. A poor representation and impossible to use for analysis because of:

5. Aliasing. This refers to the fact that the points on this plot don't show the local minima or maxima of the graph. You see those lines connecting the points? They're nonsense, just added more or less for decoration. It's hard to tell, but there may be a maxima of ~520 million at ~1500. Do you think that's a real maxima? No, it isn't. The maxima occurred at some other time. The data also isn't fine enough to contain all the structures. If I'm right about where ~1500 is, then the data shows a dip from ~520 million to ~470 million and that's it for the rest of the plot. But, as we'll see, that's not correct. So if you rely on this graph for your analysis, you're guaranteed to come to the incorrect conclusion.

I'm not aware of one, which is one of the reason that we don't look at a curve. We can, however, look at the anomalies that occurred. We know that millions were killed by disease in the New World after the Europeans arrived. Estimates vary, conservative estimates indicate that there were > 50 million native Americans before Columbus and that 85-90% of that population died as a result of the epidemics. Hispaniola had ~3 million indians in 1496 and ~11000 30 years later. So there was a great deal of loss of life. And it happened pretty quickly.

The epidemic had reached the Spanish Main by 1530. Judging by the response in Hispaniola, much of the death would have occurred by 1600. So we have a period, starting ~1500 and continuing to ~1600, with an enormous loss of life and a collapse of very large and sophisticated cultures.

Later, in China, a series of droughts and civil war were followed closely by an epidemic. The civil unrest began in the late 1630s and the epidemic lasted from 1641-1644. The estimate I've seen is that 20 million died during that period.

So how do these events coincide with the CO2 record? The link I provided earlier (http://www.skepti...ate.html ) has a pretty high resolution graph in the penultimate figure. Shortly after 1500 (1510? Watch that aliasing ;), there was a rapid drop in CO2 that correlates very well with the plague in the Americas. The data suggests that CO2 levels started to rise by 1620 at the latest. This correlates well with the rapid loss of life. Even if most of the deaths occurred prior to 1600, the sequestration of CO2 would continue until the forest had reclaimed the cultivated land.

The CO2 record then shows a second drop in CO2 levels sometime shortly before 1650 – 1640 would seem like a good estimate, but it's likely before 1650. This correlated very well with the disease in China.

The CO2 record also shows a third drop in the early 1700s. What does this correlate to? Hard to say – there were a bunch of outbreaks of plague and measles in Europe and North America from 1710-1722 (http://en.wikiped...pidemics ).

So what do we have? As you've seen the rise in CO2 correlates well with the rise in agriculture. Clearing of land for crops gives a well known and understood mechanism for this rise. Drops in CO2 levels from ~1500 - ~1800 correlate very well with known epidemics. CO2 loss due to reforestation corresponds roughly with CO2 drops seen in the glacial record . And maybe correspond very well – I admit to not having investigated the updated values and how they help to close the budget. But they're not needed to provide very good confidence that the anomalous rise in CO2 starting thousands of years ago was primarily due to humans. (I should note that Ruddiman also addresses possible natural causes. You did read that didn't you? ;)

First of all, it is problematic that the graph has no provenance, so I would welcome if you find a better one. However, we do not have anything else to go by at this time, so let's stick with for now.

Second, you are missing a crucial point. You cannot look only at the numbers of population reduction, it is absolutely necessary to relate the numbers to the population at the time. Let's us for a moment imagine that 100 million people died tomorrow, and we observed a drop in land release of carbon of 30%. What would this tell us? It would tell us that the drop probably has nothing to do with the deaths, since only 1.5% of the population vanished. Instead, in such a situation the more likely intepretation is that something else is causing the deaths and the population reduction, such as a drought that affects both crop production and carbon uptake in forrests. (That is, if there is no good reason why the 1.5% were particularly important for carbon release)

Let us look at the graph that you brought into this discussion. What you are attributing to population reductions looks more like noise to me. In the second to last graph (you referred to it), for instance, the carbon dioxide levels are essentially constant from year 200 to year 1600. This alone should disqualify the theory, because if you look above at the numbers, the population increased from ~200 million to ~600 million in this time frame.

If you remember my comment above, the CO2 emission should be somewhere between proportional to, upto integrating of the population. And, none of the extreme scenarios allow for the population to tripple and still have essentially flat-lined carbon emission. It does not compute.

Let us also take a look at the curve in the same article (to which you referred), that shows the CO2 levels increasing from ~260 ppm to 280 ppm from app. 6000 years before now to ~500 years before now. In a way this is more consistent with the population curve from Wiki, i.e. we see an effect that starts when the population curve starts to rise (6000 years before now) and not 8000 years before now, but it is at the same time completely off quantitatively.

From 6000 years before now until 4000 years before now, the CO2 levels increase by 10 PPM. This apparently happens with a global population of ~less than 30 million. But in the next 2000 years you get less than 10 PPM increase of the CO2 levels despite the fact that the population grew by at least a factor of 10!

A detail about the time frame 200 a.c. to 1600 a.c. The authors of the (flat-lined) CO2 curve indirectly admits that the population has increased. At the left side they write 10+15 million = . 12.5% of global population (==> 200 million global population) and at the right hand side they write 50+20 million =15% of global population (==>466 million global population). Yet, they do not think it is strange that the CO2 levels are more or less constant even though they themselves has estimated that the population has more than doubled!

So, I guess I have to pose the question again: How do you envision that the man made carbon release from land works? Clearly, it is not proportional to the number of people...but why would you then argue that a population reduction causes a drop of the CO2 levels? To me, the data simply does not fit your theory, so far. But perhaps you have some explanation for this (extreme) missfit of quantitative predictions to empirical data..?

To make things easier in our continued discussion, I have taken a ruler and measured the relevant data points from the graph....1500 4861594 6371656 8351750 1000...

Well, this shows that the graph is useless for the discussion. From the CO2 graph, there would need to be at least 7 points in the section under discussion - and that only if they could be cherry picked in the right locations on the graph. It also occurs to me that a global population isn't quite as useful since a given population loss in, say, northern Europe, obviously wouldn't sequester the same amount of CO2 as the same population loss in the Amazon. Really, there's absolutely no reason to be looking at the global population. It's much better to look at the amount of CO2 that dropped and see if this can be explained by either natural or anthropogenic events, like Ruddiman did.

In the second to last graph (you referred to it), for instance, the carbon dioxide levels are essentially constant from year 200 to year 1600.

This is a pretty desperate claim on your part. Have you done the statistics to show this is the case? It's obvious that you haven't. Seriously, claiming that the CO2 curve is essentially constant is silly given Ruddiman 2003.

But in the next 2000 years you get less than 10 PPM increase of the CO2 levels despite the fact that the population grew by at least a factor of 10!

You might have a point if agriculture didn't improve and urban areas didn't grow. All this would mean a more efficient use of land. Nothing you say here could be claimed to refute Ruddiman's hypothesis.

Yet, they do not think it is strange that the CO2 levels are more or less constant even though they themselves has estimated that the population has more than doubled!

Clearly, it is not proportional to the number of people...but why would you then argue that a population reduction causes a drop of the CO2 levels?

Because it must. If it didn't, it would violate pretty basic physics. Deforestation interrupts the natural carbon cycle, so CO2 levels must change - either up or down. Studies have shown that it increases, so Ruddiman's hypothesis follows the basic physics. His accounting also shows that deforestation explains the rise in CO2 as deforestation increases and the drop as reforestation occurs following the loss of large parts of the population. I get the impression you've read none of the papers on this and just disbelieve because of your personal incredulity. Just because you don't understand something doesn't make it not true.

By the way, if you are interested in the data on the correlation between reforestation due to population loss and decreasing CO2 levels, you could look at http://www.resear...conquest and http://www.resear...0000.pdf . For some reason, I can't download from the former link, but the paper is available. Take some time to read the papers before discounting the hypothesis just based on your personal biases.

... would need to be at least 7 points in the section under discussion ...

Remind me. Why is that?

... obviously wouldn't sequester the same amount of CO2 as the same population loss in the Amazon ...

Really? Can you put some numbers on that statement? Without numbers, such a statement is only hand-waving. But the authors of the article to which you referred uses several non amazonian population slumps. On the left hand (still second to last graph), they write "10 million in Europe/Meditarrean 15 millon China". Here, 25 million lost apparently explains a drop of 6 PPM CO2. On the right hand, they write "50 million in Americas, 20 million in China", which causes a 8.5 PPM drop. By implication, the authors think that every european/chinese humans contributes more to the CO2 emissions. So who is correct, you or the authors of the article to which you refer?

This is a pretty desperate claim on your part. Have you done the statistics to show this is the case? It's obvious that you haven't. Seriously, claiming that the CO2 curve is essentially constant is silly given Ruddiman 2003

I am merely looking at the graph that you have provided from your source. Still the same graph, second to last. Just before the slump at 200 A.C. I read 282 PPM. Just before the last drop (where the authors write 50 million Americas, 20 million China) at 1500 A.C., I read about - give or take 0.1 PPM - 282.5 PPM. That is, the carbon dioxide levels have increase by 0.2% in 1400 years. That is pretty much constant, wouldn't you say?

Unfair points? OK, fit a straight line to the curve, and tell me what slope you get. 0.1 PPM per thousand years? 0.01 PPM per thousand years? Again, I am only using the data that you have provided..

You might have a point if agriculture didn't improve and urban areas didn't grow. All this would mean a more efficient use of land. Nothing you say here could be claimed to refute Ruddiman's hypothesis.

So, you increase the population by approximately a factor of ten, and by chance, global population also become 10 times less wasteful of land resources per capita so the CO2 slope remains almost constant? The interesting part, though, is how gradual this technological development must have been. Population growth is exponential, but so is the technological improvement..No kinks, no jumps, no disruptions..? What a coincidence!

But I will accept the argument, but only if you can show some independent evidence that land clearing per capita and time was lower in, say, year 2000 B.C. compared to 4000 B.C. by a factor of 10 (~population difference). Source?

Because it must. If it didn't, it would violate pretty basic physics. Deforestation interrupts the natural carbon cycle, so CO2 levels must change - either up or down.

Yes, but by how much? It is that quantitative part that makes or brakes the theory of humans as the main driver of carbon emissions before industrial times. If the population can grow by a factor of ten, and the CO2 level still has a constant slope, then it would seem that it is not a very good theory. Then, you must find some other mechanism to explain the rise of CO2.

Unless, of course, you can show that some independent evidence of how much land prehistoric people cleared, and use this together with a population estimate to show that these people must have caused this carbon emission. Here, I am talking about archeological evidence and estimates of plant growth rates a.s.o. Do you have any such evidence?

Yep, you are right on this account: I have not read the papers. But you have, and presumably you have understood their arguments. So, I assume that you, having measured the pro's and the con's, you can dispel my doubts by presenting the reasons why you were convinced. I don't think that is asking to much?

Just because you don't understand something doesn't make it not true.

True, of course, but it cuts both ways. As I wrote above, you have read and understood their arguments, so you should be able to explain why, for instance, a massive population growth does not increase the rate of carbon release. When I say explain, I naturally also mean give relevant numbers to support your claim..So far, you have not been able to.

Really, there's absolutely no reason to be looking at the global population.

I disagree. If you look at the global population, you will use the data of someone that has added all the deaths and increases in population and summed it to one number for each given time with no obvious agenda. If you choose to look for some event that corresponds to a drop in the CO2 level, there is an obvious risk of unintended cherry picking. You probably would not search the literature looking for disasters when your CO2 graph is flat or going up.

So, if you use the population data, you will also know if a rapid population growth in some other part of the world (which was not struck by disease) offset the loss of lives. The trusty statistician has done all that work for you...This is why population data should be used.

I don't like lazy people and dislike intellectually lazy people even more. There's nothing wrong with being ignorant on some topics - no one can know everything. But choosing to remain ignorant on topics you want to discuss seems idiotic to me. Your objection to this isn't the physics. It's just that you can't believe it - your personal incredulity. You remain fixated by that logical fallacy and nothing will convince you otherwise.

If you look at the global population, you will use the data of someone that has added all the deaths and increases in population and summed it to one number for each given time with no obvious agenda.

Ah, yes, the conspiracy angle - always good. If you use global population, deforestation in Sweden is the same as deforestation in the Amazon - obvious nonsense.

I see no point in continuing a discussion where only I do the research.

But choosing to remain ignorant on topics you want to discuss seems idiotic to me.

But I don't remain ignorant. I get your answers, someone who has already digested the literature and understood the arguments. I just want the arguments shorter than a long winding article, that is all.

So, tell me, how come the CO2 graph is flat (see previous posts) 200 A.C. to 1600 A.C. although the population more than doubles (according to the authors of "your" article)? How come the CO2 graph is (almost) linear -4000 B.C. to 0 B.C. although the population increases exponentially in this time frame? Do you think these are unreasonable questions?

You don't need a conspiracy theory to believe in a bias towards getting your article published - and by extension - boosting your career. If you start looking for evidence that contradict your own findings, you may find it. And, the main consequence of it would be to diminish the apparent force of your article. Somehow, I don't think that the authors would put quite as much effort into this compared to the effort used proving their point. Call me a cynic if you like.

But, hopefully, the specialists at calculating world population would spend equal efforts to all years on their graphs, and would not have a particular reason to bolster/suppress the population numbers for any given time. Unless you give a reason why they should be biased..

If you use global population, deforestation in Sweden is the same as deforestation in the Amazon - obvious nonsense.

First of all, Sweden - and indeed the whole subarctic region - must have been very sparsely populated in the time frame at hand, and should therefore not influence population curves noticeably. Second, the results from "your" article seems to contradict your assumption.

There, every European death clearly causes a larger reduction per capita of the CO2 level. Your data. Thirdly, it is not clear why clearing of land in the amazonas should be more significant per capita for the CO2 level. Let me explain...

Yes, I do believe that every hectare of rain forest contains more biomass than one hectare of forest in the subarctic region. But, it could also be that the farming productivity per area in the amazonas was higher than in the cold region. Let say, for arguments sake, that a farmer in the amazon region would have to clear 1 hectares per year to support his livelihood, but a farmer in the subarctic region would have to burn/clear ten times that surface to grow sufficient calories. Then, it could actually be the farmer in the north that affected the CO2 level more per capita. Indeed, the energy needs of the northerner could be greater due to the cold climate...

This assumption could be wrong, but if you want to claim vastly different effects on the CO2 level by the Europeans compared to the Amazonians, then you have to bring the numbers..Your "teammates" - the authors of articles to which you refer - seems to make no such distinction.

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